Knowledge of one's position is required for numerous endeavors in modern life. By way of example, surveyors require precise positioning for land surveys and construction projects. Shipping companies implement tracking devices in containers requiring position information to monitor their locations. Numerous types of service companies use position information to track the locations of their service personnel as they make various service calls to ensure they're not deviating from their assignments. Drivers use knowledge of their position to obtain driving directions from one point to another and to determine the whereabouts of points of interest including hotels, restaurants, gas stations, and landmarks. This is but a small sample of the types of everyday endeavors that require knowledge of one's position on or near the earth.
A well-known system for providing such positioning information is the Global Positioning System (GPS). GPS satellites provide ranging codes to allow receivers to determine their positions. These codes are known as the coarse/acquisition (C/A) code and the precision (P) code. Each C/A code is unique to the satellite it is on and substantially orthogonal to all other C/A codes in the GPS system. Similarly, each P code is unique to the satellite transmitting it, and substantially orthogonal to all other P codes for satellites in the GPS system.
The C/A and P ranging codes are modulated onto L-band carriers L1 and L2 for transmission. The L1 carrier frequency is 1575.42 MHz and the L2 carrier frequency is 1227.6 MHz.
Using received ranging codes, a GPS receiver can determine pseudoranges from a number of GPS satellites in its view. Using the determined pseudoranges, the position of the receiver can be determined by solving a well-known set of non-linear equations. Although data from only 3 GPS satellites may be sufficient to determine position in some applications, data from at least 4 GPS satellites is preferred to account for discrepancies between the GPS and receiver clocks. While the C/A code is always available, to prevent spoofing or other man-made data corruption, the P code may be encrypted, and may not be available for general position determination.
Another position determining system planned for operation in the near future is the Galileo system. The Galileo system uses position determining techniques to those described above for the GPS system. However, the Galileo system will operate using a different signal structure than the GPS system described above.
The GPS signals described above can be detected by a GPS baseband architecture apparatus. Such apparatus can be included on an integrated circuit chip and include mixed analog and digital processing capabilities. Important in such chips is minimizing power consumption and overall layout area required for processing GPS signals. Conventional GPS baseband architectures typically use a high order filter after mixing the received GPS signal to an intermediate frequency. Such high order filters increasing the power consumption and the required layout area inside the chip. The GPS baseband architecture normally uses a high order filter after the mixer, increasing notably the power consumption and the required layout area inside the chip.
Another desirable feature of a GPS baseband architecture is flexibility. GPS is not the only satellite based positioning system. Others include the GLONASS system and the soon-to-be operational Galileo system. Consequently, what is needed is a new GPS baseband architecture that not only is efficient in terms of power consumption and space usage, but also provides flexibility to enable users to determine their position using any of a number of available positioning systems.